import java.util.ArrayList;
import java.util.Random;

public class Test {
    public static void main(String[] args) {
        System.out.println(Sysnumber());

    }

    public static String Sysnumber(){
        ArrayList<Character>list=new ArrayList<>();//character--字符类型
        StringBuffer sb=new StringBuffer();
        for (int i = 0; i < 26; i++) {
            list.add((char)('a'+i));
            list.add((char)('A'+i));
        }

        Random ran=new Random();
        for(int i=0;i<4;i++){
            //获取随机索引
            int index=ran.nextInt(list.size());
            sb.append(list.get(index));
        }
        int endnumber=ran.nextInt(9);
        sb.append(endnumber);
        char[] arr=sb.toString().toCharArray();
        int ranindex= ran.nextInt(arr.length-1);
        char temp=arr[ranindex];
        arr[ranindex]=arr[arr.length-1];
        arr[arr.length-1]=temp;
        return new String(arr);

    }
}
